Aviation Engine preheat question.

[RogueLeader]

It has been asserted to me that if the temperature is below 25 degrees, the plane must be plugged in prior to engine start.  I can not find it in any regulation or supplement.  Any help?

[PHall]

It has been asserted to me that if the temperature is below 25 degrees, the plane must be plugged in prior to engine start.  I can not find it in any regulation or supplement.  Any help?

Common sense. Cold, thick oil does not like to flow.

[RogueLeader]

Agreed.  So, the follow up question is that assuming engine heating is unavailable, how long after it gets above 25 can engines turn?

[PHall]

If you pull the oil dip stick and the oil on the end has formed a drop.
If it's warm enough to form a drop it should be warm enough to flow.
But I would not go above idle speed until the oil temp is in the green area of the oil temp indicator.

[Briank]

You really need to look at the engine manufacturer guidelines for this information (if it's not already clearly spelled out in the POH) as it is engine (and airframe, due to cooling designs) specific.  It can also vary depending on your pre-heat method, so the operating instructions for your pre-heater should be reviewed.

As a general concept though, most of the ones I've read are fairly similar.  If it's below somewhere around freezing, some kind of pre-heat is recommended.  If it's in the low teens or lower, sometimes a full 24 in a heated hangar before flight is recommended.  Also note that some airplanes have oil cooler cover requirements based on temperature.  As far as operation, don't take off until in the normal oil temperature operating range.  Some airplanes you don't even runup until in that range, others if you don't runup before then you'll never get to that range.  :-)

[Panzerbjorn]

From a Cessna 182T NAV III AFM

[Live2Learn]

It's helpful to remember that the POH minimum temperatures as posted in the C182T POH excerpt by Panzerbjorn are just that:  MINIMUMs.  Numerous other sources recommend pre-heating any time ambient temperatures fall below 32 dF, and some even suggest preheat is helpful for temperatures below 40 dF.

Regardless, preheating should be done carefully and with strict compliance with POH procedures.  Most aircraft manufactures recommend against continuous preheating, though some companies that sell specific pre-heaters assert THEIR products can be left on continuously.  For example, the TANIS Aircraft Preheat System COLD WEATHER MODIFICATION OPERATING GUIDE,  Document No: TPG0001, Rev. F at http://www.tanisaircraft.com/productattachments/index/download?id=32 recommends a minimum of six hours of preheating or continuous operation when ambient temperatures are below 32 dF. 

In any case, single point pre-heaters (for example oil pan heating pads) shouldn't be left on continuously because severe internal corrosion in the engine can occur. Other pre-heaters have similar continuous recommendations.   FWIW, I know of a very nice C185 that, because of severe pitting received a new engine after just one winter of continuous single point pre-heat.

Take a look at the Wing supplements to CAPR 66-1.  Some of them speak to pre-heating.

Cold, think oil is just one of the issues with winter operation.  Aluminum and steel expand and contract in response to temperature at very different rates.  Serious cylinder scuff can occur following cold starts where engines are cold soaked.  Low oil temperatures that congeal the engine's life blood greatly exacerbate the problem.

Preferred preheat is in a warm 40+ dF hangar.  Warm air preheaters can also effectively bring an engine to temperature quickly (an hour or two depending).  Big engines require more time to warm up than small ones, so don't assume 30 minutes of heat on a Cub will have the same beneficial effect on your O-520 Cessna powered ride.

[PHall]

Another thing the "warm" hanger does is it warms up the fuel system. Ice crystals in the fuel filter is not a good thing.
Frozen sump drains are no fun too.

[Panzerbjorn]

Another thing the "warm" hanger does is it warms up the fuel system. Ice crystals in the fuel filter is not a good thing.
Frozen sump drains are no fun too.

Nothing a cigarette lighter won't fix...

[PHall]

Another thing the "warm" hanger does is it warms up the fuel system. Ice crystals in the fuel filter is not a good thing.
Frozen sump drains are no fun too.

Nothing a cigarette lighter won't fix...

Could you please demonstrate that on your plane while I watch from across the ramp? Thx!

[Luis R. Ramos]

How many fire extinguishers do you reason his little demonstration with the lighter will require?

[docsteve]

Spark plugs are an additional issue: a failed start may leave sufficient condensed water vapor in the cylinder to freeze across the electrodes if the surface temperature of the plugs is below freezing.  Once that happens, the plugs probably need to be removed to be thawed.

[scooter]

It not about the oil. Its about the different metals in the engine not expanding at the same rate when its cold. Read the attached.

[PHall]

It not about the oil. Its about the different metals in the engine not expanding at the same rate when its cold. Read the attached.

Oh, it's all about the oil. Because if it doesn't flow you will have those different metals in the oil filter along with a damaged or seized engine.